1. Field of the Invention
The present invention pertains to surfactant compositions for wellbore operations and methods for formulating such compositions from alkyl polyglycoside surfactants and linear ethoxylated alcohol surfactants which form Winsor type III microemulsions, in selected oil/water systems and which are particularly useful in wellbore operations.
2. Background
The failure to perform an effective cleanout operation during drilling or workover of an oil or gas well, or an acidizing treatment of a formation interval, or to establish a bond between a cement composition and a wellbore wall or a casing or tubing can cause undesirable results in oil and gas well operations. For example, failure to perform an effective cleanout operation during drilling or workover of an oil well can result in contamination and plugging of an earth formation from which fluids are desired to be produced. Moreover, during an acidizing treatment of an earth formation to make the formation more productive, if oil based contaminants in the formation interval adjacent to a wellbore are not removed therefrom the effectiveness of the acidizing treatment can be substantially reduced. Still further, ineffective cleaning of a wellbore wall, including a casing, liner or tubing string, can result in a poor cement bond during cementing operations thereby allowing an undesirable flow of fluids along the wellbore or a failure to stabilize the casing in the wellbore. The cost of remedial action for any of the above-mentioned failures can be substantial in both onshore and offshore well operations. Moreover, contamination of a formation interval with unwanted oil based materials can be ruinous.
U.S. Pat. No. 5,374,361, issued Dec. 20, 1994 to Albert F. Chan, is directed to providing an improved method of removing oil based material from a wellbore using a washing composition containing an alkyl polyglycoside surfactant which comprises 1.0% to 10.0% by weight of the composition and with a co-surfactant selected from a group consisting of linear alkyl ethoxylate and alkyl phenol ethoxylate. Still further, U.S. Pat. No. 5,458,197, issued Oct. 17, 1995 to Albert F. Chan is directed to improved cleanout systems for wellbores using alkyl polyglycoside surfactants. Both these patents are hereby incorporated in their entirety by reference. Notwithstanding the improvements in well cleanout operations described and claimed in these patents, there has been a need to provide a cleanout composition which has suitable characteristics for solubilizing substantially all of the oil based materials expected to come into contact with the composition. Moreover, this solubilization characteristic should be substantial while providing a range of a hydrophilic-lipophilic balance of the composition as broad as possible, since, for example, the salinity of fluids present in a well and an adjacent earth formation may vary considerably. Accordingly, the range of the microemulsion formed by the surfactant solution, as a function of the hydrophilc-lipophilc balance (HLB) is desired to be made as broad as possible.
Alkyl polyglycoside surfactants in electrolyte solutions having a pH of about 4.0 or less have good wettability, suspension of contaminant particles and solubilization of oily coatings on surfaces. The acidic nature of cleaning solutions of this type is such as to also show a distinct capability of dissolving carbonate and calcite scales and iron oxide. Solutions of alkyl polyglycoside surfactants, in combination with caustic materials such as sodium hydroxide and potassium hydroxide, are also particularly effective in removing oil based drilling fluids, pipe thread sealant and lubricant materials and other oil based contaminants found in wellbores, including diesel oil, mineral oil, synthetic oils and crude oil as well as other naturally occurring hydrocarbon substances. Alkyl polyglycoside surfactants remain very surface active at relatively high pH and therefore can be used effectively as wetting, dispersing and/or emulsifying agents in a caustic environment, such as encountered in cement slurries, for example. Moreover, alkyl polyglycoside surfactants remain active at relatively high temperatures, up to about 350.degree. F., for example, because alkyl polyglycoside molecules have a superior hydrogen bonding capability as compared with other typical nonionic surfactants such as ethoxylated alcohols.
The oil soluble portion of alkyl polyglycoside surfactants may be controlled by the alkyl chain length which can be varied from about C4 to about C20. Each saccharide group is believed to be equivalent to five to seven ethylene oxide groups in ethoxylated alcohol surfactants and is therefore very effective in rendering water soluble properties to alkyl polyglycoside surfactants even at high temperatures and the high salinity and hardness conditions found in sea water and subsurface brines, for example. Moreover, since oil, brine and the above-mentioned contaminants are usually present in an oil well, for example, it is desirable to provide an alkyl polyglycoside composition for well cleanout and formation interval decontamination, which exhibits very low interfacial tension and forms a Winsor type III microemulsion over the broad temperature ranges typically encountered in both shallow and deep oil and gas wells.
Still further, since the temperature or the salinity of fluids present in a well may vary considerably, the range of the microemulsion formed by a surfactant composition, as a function of the HLB is, as mentioned previously, desired to be made as broad as possible. Additionally, the breadth of the middle-phase or Winsor Type III microemulsion, as a function of the HLB number is also desired to be made as broad as possible.
Although alkyl polyglycoside surfactants have become popular in various detergent compositions, primarily directed to institutional and household cleaning products which are not exposed to the extremes encountered in wellbore cleanout processes, these products have been developed with relatively short alkyl chain length surfactants from C4 to C10 which do not provide sufficient emulsifying properties to emulsify oils frequently found in wellbores. On the other hand, relatively long alkyl chain length surfactants such as C16 to C18 which do not provide sufficient wetting properties have been used in emulsified cosmetic cleansing products. Further the longer alkyl chain length alkyl polyglycosides, especially the polyglycosides containing an even number of carbon atoms, are surfactants which are too viscous for convenient mixing to provide surfactants to meet varied wellbore conditions. The compositions with the shorter alkyl chain lengths act as good hydrotropes or wetting agents and the compositions with the longer alkyl chain lengths have good emulsifying properties, but none of these commercially available compositions, used alone, are deemed optimal for conditions wherein a relatively broad range of salinity of wellbore fluids and a relatively broad operating temperature range are encountered. Accordingly, there has been a pressing need to develop improvements in alkyl polyglycoside surfactant compositions used generally in the methods and systems described in earlier patents as well as in other well operations and related activities wherein oil based contaminants commonly found in wells are present and are desirably removed.